The Viral Studies Section (VSS), Viral Epidemiology Branch (VEB), Epidemiology & Biostatistics Program (EBP), Division of Cancer Etiology (DCE), National Cancer Institute (NCI), is continuing the conduct of this study to define, through a series of epidemiologic, clinical and experimental studies, the distribution and determinants of HTLV infection and the possible role of HTLV as a cause of cancer. An important future direction is to follow-up infection for both HTLV and HIV, and use these high risk populations to define the natural history and pathogenesis of viral-related outcomes.